A new digital channel bank has been designed to obtain a more economical interface between the No. 1 ESS machine and T-carrier facilities by obliterating the traditional interface between switching and transmission circuits. The predecessor arrangements were predicated on a standard interface for all carrier and metallic trunks. These used multiple leads for each trunk between the trunk relay circuits and the carrier terminals via an Intermediate Distribution Frame (IDF) to exchange signaling and supervisory information. The No. 1 ESS common control interfaced the trunk relay circuits directly for each relay and ferrod sensor via a signal distributor and scanner, respectively.
The newly designed, digital channel bank replaces the earlier carrier terminal, trunk relay circuits, scanner, and signal distributor with a single integrated frame. This design also eliminates the IDF and the need for the per-trunk leads to interconnect the earlier separate trunk relay circuits and carrier terminals.
In this new channel bank design, a controller unit communicates over a shared bidirectional data bus with up to twenty-four (24) channel units. A great deal of data is presented to (and by) the channel units and this information must be transferred to the controller. For example, it is necessary that each channel unit report the following data to the controller: received signaling status; loop closure status; maintenance status; channel unit relay status, et cetera. The task is aggravated by the fact that only a few leads (e.g. four) are available in the back plane of the channel banks for use in data transfer between the channel units and the controller.
Techniques have been adopted to improve the efficiency of the data handling process. For example, reporting only highest priority data can be used to obtain a more efficient data transfer method. Nevertheless, to meet the data transfer-time constraint presented, the quantity of data carried by the shared bidirectional data bus must be minimized.